Q.(a) State Henry's law.

Solubility is the amount of solute a saturated solution holds per unit volume, at a specific temperature -- the solute's maximum achievable concentration in that solvent at that temperature, usually expressed in mol L-1. A solution reaches saturation through a dynamic equilibrium between dissolution and crystallisation; adding solute beyond this point (a supersaturated solution) is unstable and will precipitate the excess if disturbed. Three factors govern solubility: (1) the chemical nature of solute and solvent -- 'like dissolves like', since similar intermolecular forces favour mutual solubility; (2) temperature, whose effect depends on whether that solute's dissolution is endothermic (solubility rises with temperature, by Le Chatelier's principle, e.g. KCl) or exothermic (solubility often falls, e.g. Na2SO4) -- though this is not a strict universal rule; (3) pressure, which has no effect on solids/liquids (incompressible) but strongly governs GAS solubility via Henry's law, $S=K_HP$ -- the solubility of a …